SCREW n.
specially of the genus Turritella and allied genera. See Turritella. -- Screw steamer, a steamship propelled by a screw. -- Screw thread, the spiral which forms a screw. -- Screw stone (Paleon.), the fossil stem of an encrinite. -- Screw tree (Bot.), any plant of the genus Helicteres, consisting of about thirty spe…